Frankfurt  - Stock in Volkswagen AG shot 27 per cent higher Thursday as a mystery buyer scooped up shares in Europe's biggest carmaker, which is at the centre of a battle for control.

The stock ended electronic trading in Frankfurt at 304.00 euros.

Luxury car maker Porsche declared this week that Volkswagen had effectively become its subsidiary. Porsche controls 35 per cent of VW. But the German state of Lower Saxony contends its 20-per-cent stake gives it veto rights to obstruct Porsche.

Both Lower Saxony and the Porsche family would thus have a motive to buy stock from independent shareholders.

"Porsche is not active on the market, so it's not buying Volkswagen stock," a spokesman for the Porsche company said.

"We have options to buy stock, but there is no need to do so now," said a spokesman for the Lower Saxony state government in Hanover. "We won't discuss speculation."

Observers said such a massive jump in the price of a top German stock was almost unprecedented, especially when other shares are down amid financial market turmoil since the Lehman Brothers failure.

Frank Schwop, an analyst with public bank Nord/LB, suggested a third party might be buying shares to settle a futures trade with one of the two big shareholders.

Others suggested Lehman Brothers might be attempting to unwind a deal involving the stock.

Lower Saxony has hinted it may increase its stake in Volkswagen to 25 per cent, the usual threshold for veto rights, if the European Union obliges Germany to repeal legislation that grants Lower Saxony special veto powers with its lesser stake. (dpa)